Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $151.39   10.122%   $166.7137   $166.71   $166.70   $166.70  
  Purchase #2 $223.98   10.840%   $248.2594   $248.26   $248.25   $248.30  
  Purchase #3 $66.43   10.116%   $73.1501   $73.15   $73.15   $73.20  
  Purchase #4 $43.58   6.130%   $46.2515   $46.25   $46.25   $46.30  
  Purchase #5 $154.87   6.314%   $164.6485   $164.65   $164.65   $164.60  
  Purchase #6 $152.58   9.508%   $167.0873   $167.09   $167.10   $167.10  
  Purchase #7 $19.29   5.314%   $20.3151   $20.32   $20.30   $20.30  
  7 purchase totals = $812.12       $886.4256   $886.43   $886.40   $886.50